Synergistic fluid energy reducing and classifying unit



Sept. 20, 1960 H. G. LYKKEN ETAL 2,953,307

SYNERGISTIC FLUID ENERGY REDUCING AND CLASSIFYING UNIT Filed Oct. 15,1956 2 Sheets-Sheet 1 llzmcy 0. Aykkzw y M4414 Lyme/v lrrazwsm- Sep t.20,1960 GQLYKKIIEN E AL 2,953,307

'SYNERGISTIC FLUID ENERGY REDUC NG AND ,CLASSIFYING UNIT FiledOct.15;;195e 2 Sheets-Sheet 2 INVENTOR. l/EA/Ry 6 imam-w BY [mu/4n ll.Amen-w ez/ www A rrokmsr;

United States Patent O SYNERGISTIC FLUID ENERGY REDUCING AND CLASSIFYINGUNIT Henry G. Lykken, Minneapolis, and William H. Lykken, Edina, Minn.,assignors to The Microcylclomat Co., Minneapolis, Minn., a corporationof Delaware Filed Oct. 15, 1956, Ser. No. 615,923

11 Claims. (Cl. 241-52) This invention relates to the reduction andclassification of dry solid materials. More particularly this inventionrelates to an open rotor fluid energy mill with centripetal extractionclassification for the reduction of dry material to any specifiedparticle size and finer in the subsieve range.

The reduction of any material on a commercial scale to specific particlesize and finer in the subsieve range is an art. It is an art whichrequires its own essential techniques, processes, methods and means. Itis not an art which can be practiced merely by the provision of a millplus a classifier. More than this is required. Of necessity, there isrequired a complex and completely integrated unit of manyinterdependentelements, parts and processes, which, because of their interdependencecan only act as a unit and must be so considered.

It is a well known and universally accepted fact, that in any grindingoperation, the accumulation of fines, particularly subsieve material, inthe mill load has a retarding and cushioning effect. Ten percent offines in the mill load will reduce the mill capacity 50% or more. Thisreduction in mill capacity increases at an accelerated rate as the finesincrease. The rate will. vary with the character of the material beingreduced but doubles and redoubles in eifect as the desired cut sizebecomes finer, until further reduction becomes negligible.

So, in milling practice, with any kind of mill, the fines must becontinuously removed from the mill load. Milling efficiency depends onthe completeness of this removal, since no fines (that is, material ofthe wanted particle size and finer) in the mill load is the optimumcondition for maximum reduction.

En masse, finely divided material acts like a fluid, made up as it is ofparticles with little body and negligible mass. It yields to impact andpressure with negligible internal friction and partiole-on-particleabrasion. It acts more like a fluidal lubricant. Any material, afterreaching a certain fineness seems to evade further reduction by normalmethods and means of grinding. Maximum efliciency in milling requiresnot only efficient reduction means, but interacting classifying means toassist the reducing means by continuously and instantaneously removingthe wanted particle size and finer from the mill load and continuouslyreturning the oversize for further reduction. At the same time, in orderto achieve a greater rate of reduction and a greater degree of finenessit is necessary that the material particles be highly dispersed in air,uniformly and independently.

The invention is illustrated by the drawings in which the same numeralsrefer to corresponding parts and in which:

Figure 1 is an end elevation, in section, of the synergistic fluidenergy reducing and classifying unit of this invention, the sectionbeing taken along the line 1--1 of Figure 2 and in the direction of thearrows; and

Figure 2. is a side elevation, in section, taken on the line 2-2 ofFigure 1 and in the direction ofthe arrows.

The reducing element of the synergistic unit comprises a lowerhorizontal axis peripheral inlet and peripheral discharge closed endrotor 10, preferably including an assembly of like closed end rotorunits 11.

The rotor is contained in a reducing chamber enclosed by a generallycylindrical housing 12 around about threefourths of the periphery of therotor. Housing 12 is held between two end plates 13 and 14 which extendto a base or floor and are afiixed by floor flanges.

A suitable bearing structure adequately sized to carry the reducingrotor is mounted at each end of the housing outside of the end plates.Upon these bearings there is mounted a shaft 15 which carries thereducing rotor. Shaft 15 is driven by any suitable drive means, notshown. The shaft is enlarged and reinforced through part of its lengthby a tube 16 supported by annular rings 17 welded or otherwise securedto sleeves keyed to the shaft. The shaft, tube and annular rings form arigid unitary structure upon which the reducing rotor units 11 aremounted.

The closed end rotor units 11 are comprised of a slotted annular disk 18perpendicular to the shaft and carrying a plurality of flat radialblades 19 around its periphery. Radial blades 19 are positionedperpendicular to the slotted disk and each unit is enclosed between apair of disks 20 having diameters reaching to the periphery of blades19. A series of rotor units is mounted on the rotor between a pair ofrotor end disks 21 mounted on each end of tube 16 and secured to theannular rings. The disks 18 and '20 are supported by a plurality ofbolts 22 extending between end disks 18 and surrounding tube 16. Thedisks are held spaced apart by spacers 23. 1

The reducing rotor 10 develops a relatively high axial vacuum due to ahigh centrifugal discharge on the forward or leading face of each blade19 and to the Velocity of recession at the back of each blade. Thisvacuum drags air and material into the rotor at the back of each bladewith a velocity considerably higher than the peripheral velocity of therotor itself and discharges the air and material on the forward face ofthe next or trailing blade. There is set up a high velocity in-and-outflow between each pair of blades which induces an intense fluid energyvortex between the blades, and, at the same time, corresponding unitvorticose flows in the fluidal material circulating around the rotor.

The reducing rotor 10 is mounted in the housing 12 with a runningclearance of two inches, more or less (that is, between about 1 and 3inches depending upon material, velocity, volume of air, etc.), betweenthe periphery of the rotor and housing wall around about three-fourthsof the periphery of the rotor. The mill load is maintained in a highlyfluidal condition, such as, for example, one part solids by volume toabout 6 to 12 parts of air, and, preferably, one part solids by volumeto about 8 tolO parts of air. i

The fluidal mill load circulates at moderate velocity with the-rotor andis continuously and repeatedly sucked into and discharged by the motor.Particles which are too large to enter into the rotor are nibbled downby blade impact until they are of a size which does enter. Then they areprogressively reduced by repeated blade impact each time they enterand/or discharge.

The primary reduction of the dry solid material is a shearing actioncutting edge rotor blades are used. The mill housing is split so the topcan be lifted off and the rotor lifted out and turned end for endperiodically to provide a self-sharpening blade wear.

The mill feed enters the reducing rotor chamber tangentially at inlet 24below the axis of the rotor along its full length in a regulated amountfrom an elongated feed hopper 25 to maintain a desired bulk or weight ofmaterial in the circulating mill load. The feed is preferably regulatedby an interlock between the motor operating the metering closure 26 ofthe feeder and the reducing rotor motor so as to regulate the feedermotor to maintain a uniform mill load. The mill load can be set at anydesired fluidity or material to air ratio in the circulating flow. Airis admitted through air duct 27 with the material feed, so regulated, asby a slide damper 28, that upon every revolution of the rotor all of thewanted particle size and finer is continuously carried out of thecirculating load with a minimum of oversize.

The lower reducing rotor acts as a powerful peripheral fan. It has aperipheral inlet with a substantial suction into which the air andmaterial is fed, and a high velocity peripheral discharge at the top.This provides for several independently controlled, but interacting,synergistic air .flows in the reducing and classifying unit as a whole.

The fixed air content in the reducing chamber is circulated by andaround the lower reducing rotor continuously. The air drawn into thereducing chamber by the rotor is discharged into an open chamber 29 atthe top of the rotor with high velocity pressure, thence up into theclassifying chamber 30, over the upper classifying rotor 31 and into acirculating flow around it. Part of this air flow follows the peripheralwall 32 of the classifying chamber down through a skimmer gate 33 forthe return of oversize to the reducing rotor where it receives anadditional velocity impulse and suction drag by the reducing rotor andrecirculates.

This circulation is controlled by the swimmer gate 33 which comprisesthe space between classifier chamber wall 32 and the beveled edge of anelongated plate 34. Plate 34 slides between a horizontal support 35which extends the length of chamber 30 spaced apart from the back walland between hold down plates 36 on the end walls 37 and 38 at theopposite ends of the chamber. The beveled edge of plate 34 has at leasttwo rods 39 projecting from it and passing out through tubes 40 on theoutside of the chamber wall. At least one of rods 39 is preferably screwthreaded and provided with -a threaded thumb wheel 41 (between two fixedcollars 42) by which plate 34 may be moved and the width of the skimmergate may be adjusted.

The air from the reducing chamber circulating around 'the classifierrotor 31 enters the rotor radially and goes out axially. It is, however,only part of the air required for classification, usually the lesserpart. Supplemental air is admitted through an adjustable opening 43 intothe classifier duct or open chamber 29 between the reducing andclassifying chambers to mingle with the air flow from the reducingchamber. A slide damper permits ready adjustment of this supplementalair flow.

The upper classifying rotor 31 is an assembly of spaced slotted annulardisks 44 and spaced radial blades 45 intersecting the disks. The inneredges of spaced disks 44 define an annular axial outlet duct 46 from therotor. The disks 44 are supported at the periphery of duct 46 by aseries of closely spaced rods or bolts 47 which form inlet-outlet portshaving a uniform air resistance.

The upper rotor 31 is contained in a classifying chamber 30 enclosed bya generally cylindrical housing 32 around about three-fourths of theperiphery of the rotor. Housing 32 is held between two end plates 37 and38 which rest upon the tops of end plates 13 and 14, re-

spectively, of the reducing chamber housing. End plates 37 and 38 eachhave an annular opening through which .a central rotor shaft 48passesand thro g Which the 4 axial duct 46 of rotor 31 communicates withdischarge means.

Spaced apart from the classifying chamber housing 32 at each end is afan housing 49 including a cylindrical wall 50 held between an inner endwall 51 having an annular opening corresponding to that in classifierend walls 37 and 38, and an outer end wall 52. A suitable bearingstructure adequately sized to carry the classifier rotor and fans ismounted at opposite ends of the fan housings outside of the end plates.Shaft 48 is mounted on these bearings. It may be driven by an suitabledrive means. The shaft 48 is enlarged and reinforced through part of itslength by a tube 53 supported by sleeves 54 keyed to the shaft. Sleeves54 also support annular fan disks 55 upon which fan blades 56 aremounted.

Rods 47 extend between fan plates 54. The portion of the rotor withinhousing 32 is supported between end disks 57. Further end disks 58 aresupported by rods 47 in the spaces between the end walls 37 and 38 ofthe classifier chamber housing and the inner end walls 51 of the fanhousings to suppress any air flows which might otherwise be inducedaround the ends of the rotor.

Depending upon the length of the synergistic reducing and clasisfyingunit either one or two fan units may be used. Where two fans. are used,as illustrated, a further disk 59 is mounted on tube 53 of the rotor todivide axial duct 46 into two parts and to direct air flows to one fanor the other.

The entire air flow through the classifier rotor (as distinguished fromflows within the classifying rotor and chamber) is a function of anindependently driven exhaust fan (not shown) associated with a standardcollector system and having ample static capacity. The classifier rotordischarges into the fan housing 49, which acts as an outlet box. The fanhousing is provided with a discharge duct 60 by which it is connected tothe collector system. The centrifugal fan unit in the outlet box isprimarily an axial suction or flow equalizer having some incidental faneffect. In the suction line between the outlet box and exhaust fan (notshown) is a precise air flow regulating device. Variationin air flowregulates the pardrawing bits'of sand, stone, grit, metal and likeextraneous heavy material from the mill load. Initially, this grit trapwill become filled with the material to be reduced, but as grit and likematerial is introduced into the reducing chamber along with the feed, itwill, because of its greater density, drop to the bottom of the trap.

As shown here, the outer edge of damper 63 is ,supported by a splinedshaft or a shaft bearing spur gears 64 whose teeth mesh with the teethof racks 65 on the lower surface of the slide damper. The shaft bearingthe spur gears is suitably provided with a lever or crane handle foradjusting the slide, or preferably is provided with a variable speeddrive synchronized with the feeder drive to discharge a predeterminedfixed percentage of the feed through the grit trap.

.As already noted, the classifier rotor 31 is arranged to rotate at aregulatable peripheral velocity in the direction of the air flow aroundit. It is a peripheral inlet, axial outlet centripetal extraction rotorarranged to operate on a progressive particle size selection principle.This rotor has many and diverse functions.

In fine particle classification the material must be thoroughly aerated.Each and every particle must be enclosed in a film of air and beindividually and uniformly dispersed inthe carrier air. This is a factorwhich is often overlooked but is absolutely essential to preciseclassification. In the synergistic apparatus of this invention aerationo f the particles is afunction of the reducing rotor and the materialenters the Classifying chamber thoroughly aerated.

Additional air must then be added to provide the proper dilution. Thefiner the material the more air is called for. This air is admitted inregulated amounts through air inlet 43. The material must be uniformlydistributed in the air, and equally important, it must be maintaineduniformly distributed as it circulates around the classifier rotor.These are both functions of that rotor.

The classifier rotor has the same in-and-out flow between each pair ofblades, the same intra-blade vortex action and vorticose air flow in thecirculating air flow around the rotor as the reducing rotor has, andmore so. It maintains the perfect mixture of air and material.

The classifier rotor is rotated at a peripheral velocity to provide thedesired centrifugal throw-out effect or g in the circulating flow andwithin the rotor itself, pro portional to particle size and mass. Thisis a third function of the classifying rotor. By virtue of its partialaxial vacuum and intra-blade vortex action, it continuously withdrawsand expels the circulating fiow of material, uniformly distributed inthe air. This is done selectively with the particles of smallest sizeand least mass entering farthest into the rotor, particles of somewhatlarger size and greater mass entering somewhat less far into the rotor,etc. That is, the fines enter the rotor to a radial depth inverselyproportional to their mass. This is a fourth function of the classifyingrotor and is independent of any air drawn into the rotor. Thecirculating material continuously and repeatedly enters the rotor anddischarges. Most of the oversize circulating on the classifier chamberwall is continuously skimmed off at gate 33 and returned to the reducingchamber through duct 61. The oversize and the circulating air flow isdischarged tangentiall-y into the peripheral flow of the reducing rotoron the principle of a suction ejector as a means of maintaining thiscirculating flow.

If no air is drawn through the rotor, no material gets through. A traceof air allows only a colloidal smoke through. As the air flow throughthe rotor increases the particle size increases proportionally.Precision air flow control provides precision particle size control,provided the other functions of the classifying rotor are present.

As an example, if the desired particle size is 7 microns and finer nolarger particles should be permitted to pass through the classifierrotor. The unit is set by regulation of the air flow through theclassifier to pass 7 micron material and finer, but with a wide marginof safety. It is set so as to pass only a small percentage of theparticles as large as 7 microns in the material that continuously andrepeatedly comes to the cut-off line within the classi fier rotor. Theparticles of desired size and finer may be presented to the cut-off lineas often as a hundred times a second. It is only necessary to pick offand withdraw a few of these particles on each circuit into the rotor.Eventually all come in with no chance for oversize to get in. Particlesfiner than 7 microns are withdrawn on their first pass into theclassifier rotor.

The accomplishment of this desired precise classification on acommercial scale, of course, requires ample volumetric capacity,diameter and length of rotor. It calls for a multiplicity of annulardisk channels proportional to the capacity wanted. Preciseclassification can be achieved in the particle range down toall minusone micron.

The classifying rotor can be operated at a relatively low rotativevelocity and with relatively low air flow velocity and with maximumprecision of flow control,

(in a highly fluidal suspension and uniform individual particledispersion in a gas, such as air) to two opposing forces: first, thedrag of the suspending gas drawn cen-' t-ripetally into a peripheralinlet, axial outlet centripetal extraction rotor (Stokes law); theother, centrifugal force on each individual particle, which isproportional to the mass of the particle.

The centrifugal force can be adjusted to any desired value by varyingthe speed of the rotor. For operation, it is preferably set for aconstant value, such as from about 1000 to 2000 g at the periphery ofthe rotor, varying somewhat with the specific gravity of the materialand particle size to be extracted. As an example, a rotor 30 inches indiameter rotated at 1530 r.p.m. has a centrifugal force of 1000 g at itsperiphery. Particle size control then becomes merely a matter of preciseregulation of air volume through the classifier.

The method of reducing and classifying dry solid material according tothis invention may be illustrated as follows: A controlled supply of drysolid material to be reduced is fed tangentially downwardly into thereducing housing in which the reducing rotor is rotating. The reducingrotor acts as a fan which induces the feed and air into the housing,circulates it around the rotor while subjecting the material to highvelocity impact and fluidal vortex action, and induces a circulatingflow of air in the classifying chamber for carrying the fines up and outof the reducing area and for returning rejected oversize material to thereducing rotor for further reduction. The reduced material is carriedupwardly in a highly aerated suspension and introduced tangentially intothe classifier housing in which the classifying rotor is rotating. Theclassifying rotor acts to induce air in through the auxiliary air inlet,to further dilute the gaseous suspension of reduced particles, touniformly distribute the particles in the suspension and to maintain theuniform distribution while circulating the stream of particles aroundthe rotor, subjecting the particles to controlled centrifugal stressesand to selectively segregate the circulating particles. The desiredfines are withdrawn axially by suction through the classifying rotor toa collector system and the rejected oversize particles are skimmed offthe classifier housing wall and returned in the circulating air streamto the reducing rotor. The fan action of the reducing rotor creates asuction which withdrawsthe oversize and returns it for furtherreduction.

It will be seen that the assembly as a whole is simple in design, ruggedin construction, low in power and maintenance costs, extremelyaccessible, elemental and almost automatic in operation, with precisionperformance.

It is apparent that many modifications and variations of this inventionas hereinbefore set forth may be made without departing from the spiritand scope thereof. The specific embodiments described are given by wayof example only and the invention is limited only by the terms of theappended claims.

We claim:

1. A synergistic fluid energy reducing and classifying unit comprisingreducing means including a peripheral inlet, peripheral discharge,closed end reducing rotor mounted to rotate in a horizontal cylindricalhousing, said rotor including a shaft, a plurality of spaced apart discsmounted perpendicular to said shaft and a plurality of intersectingradial blades parallel to the shaft and perpendicular to said discscarried at the periphery of said discs, said discs dividing the rotorinto a plurality of separate rotor units, the running clearance betweenthe periphery of said rotor and the cylindrical wall of said housingbeing of the order of from about 1 to 3 inches to provide for a highlyfluidal mill load of from about one part solids to about 6 to 12 partsair by volume, a tangential inlet to said housing for material to bereduced and air, said inlet being disposed along the length of saidhousing and at about the level of the axis of the reducing rotor, meansassociated with said inlet for regulating the rate of material feed andair flow, a tangential reduced material and air outlet above saidreducing rotor; classifying means integrated with the reducing means andsuperimposed upon it, said means comprising a peripheral inlet, axialoutlet, centripetal extraction classifying rotor mounted to rotate in ahorizontal cylindrical housing, a tangential reduced material and airinlet to said housing connected with the reduced material and air outletof said reducing means, and a tangential return duct from said housingto return oversize material to the reducing rotor.

2. A reducing and classifying unit according to claim 1 furthercharacterized in that an axial exhaust chamber is associated with theclassifying means.

3. A reducing and classifying unit according to claim 1 furthercharacterized in that the tangential reduced material inlet of theclassifier inlet is provided with an auxiliary air inlet and air flowcontrol means.

4. A reducing and classifying unit according to claim 1 furthercharacterized in that an adjustably movable skimmer gate is provided insaid tangential return duct to regulate the desired volume of flowcirculating around the classifying rotor.

5. A reducing and classifying unit according to claim 1 furthercharacterized in that said classifying rotor is comprised of an assemblyof spaced annular disks and spaced intersecting radial blades formingradial ducts opening into an axial outlet duct, said axial duct having aperipheral wall of spaced rods defining inlet ports from the radialducts.

6. A classifying unit comprising a peripheral inlet, axial outlet,centripetal extraction classifying rotor made up of an assembly ofspaced annular disks and spaced intersecting radial blades formingradial ducts opening into an axial outlet duct, said axial duct having aperipheral wall of spaced rods defining inlet ports from the radialducts, said rotor mounted to rotate in a horizontal cylindrical housingof substantially larger diameter, a tangential inlet duct at the bottomof said housing for reduced air borne material, a tangential dischargeduct from said housing adjacent to said inlet duct for rejection ofoversize particles, both of said tangential ducts being the full lengthof the housing, and an axial exhaust chamber at at least one end of saidaxial duct.

7. A classifying unit according to claim 6 further characterized in thatsaid tangential inlet duct is provided with an auxiliary air inlethaving an inlet air control.

8. A classifying unit according to claim 6 further characterized in thatsaid tangential discharge duct is provided with an adjustably movableskimmer gate to regulate the desired volume of flow circulating aroundthe classifying rotor, said skimmer gate being the full length of thehousing.

9. A synergistic fluid energy reducing and classifying unit comprisingreducing means including a peripheral inlet, peripheral discharge,closed end reducing rotor mounted to rotate in a horizontal cylindricalhousing, the running clearance between the periphery of said rotor andthe cylindrical Wall of the housing being of the order of from about 1to 3 inches to provide a highly fluidal mill load of from about one partsolids to about 6 to 12 parts air by volume, a tangential inlet to saidhousing for material to be reduced and air, said inlet being disposedalong the length of the housing and at about the level of the axis ofthe reducing rotor, means associated with said inlet for regulating therate of material feed and air flow, a tangential reduced material andair outlet above said reducing rotor; classifying means integrated withthe reducing means and superimposed upon it said means comprising aperipheral inlet, axial outlet, centripetal extraction classifying rotormounted to rotate in a horizontal cylindrical classifying rotor housing,said rotor being made up of an assembly of spaced annular disks andspaced intersecting radial blades forming radial ducts opening into anaxial outlet duct, said axial outlet duct having a peripheral wall ofspaced rods defining inlet ports from the radial ducts, a tangentialreduced material and air inlet to said classifying rotor housingconnected with the reduced material and air outlet of said reducing,means, an auxiliary air inlet in said tangential inlet t0 theclassifying rotor housing, air flow control means for said auxiliaryinlet, a tangential return duct from said classifying rotor housing toreturn oversize material to the reducing rotor, an adjustably movableskimmer gate in said return duct to regulate the desired volume of flowcirculating around the classifying rotor and at least one axial exhaustchamber associated with the classifying means to connect the axialoutlet of the classifying rotor with an exhaust fan, air flow regulatingmeans and a material collector system.

10. A classifying unit comprising a peripheral inlet,

axial outlet centripetal extraction classifying rotor made up of anassembly of spaced annular disks and spaced intersecting radial bladesforming radial ducts opening into an axial outlet duct, said axial ducthaving a peripheral wall of spaced rods defining inlet ports from theradial ducts, said rotor mounted to rotate in a horizontal cylindricalhousing of substantially larger diameter, a tangential inlet duct at thebottom of said housing for reduced air borne material, an auxiliary airinlet in said tangential material inlet duct, air flow control means forsaid inlet, a tangential discharge duct from said housing adjacent tosaid inlet duct for rejection of oversize particles, both of saidtangential ducts being the full length of the housing, an adjustablymovable skimmer gate the full length of the housing to regulate thedesired volume of flow circulating around the classifying rotor and atleast one axial exhaust chamber in communication with the axial outletof the classifying rotor.

11. A synergistic reducing and classifying system comprising ahorizontal generally cylindrical reducing housing; a horizontalgenerally cylindrical classifying housing superimposed upon the reducinghousing; an interconnecting tangential outlet duct from said reducinghousing and tangential inlet duct to said classifying housing betweensaid housings; an air inlet in said inlet duct; an interconnectingtangential outlet duct from said classifying housing and tangentialinlet duct to said reducing housing between said housings; a tangentialmaterial and air inlet to said reducing housing and an axial materialand air discharge from said classifying housing; closed end rotor meansmounted to rotate on a horizontal axis in said reducing housing to actas a peripheral inlet and peripheral discharge fan to induce air andmaterial into the reducing chamber, to circulate air and material aboutitself and induce high velocity impact and a fluidal vortex action, andto induce a circulating flow of air up through the tangential outletduct of the reducing housing and the tangential inlet of the classifyinghousing, around the outer periphery of the classifying housing and downthrough the tangential outlet duct of the classifying housing and thetangential inlet of the reducing housing; peripheral inlet, axialoutlet, centripetal extraction rotor means mounted to rotate on ahorizontal axis in said classifying housing to induce supplemental airfrom the air inlet in the tangential inlet to the classifying housing,to dilute and maintain a uniform suspension of reduced particles in air,to maintain the uniform distribution of particles While circulating thesuspension around the rotor means, to subject the particles in thesuspension to controlled centrifugal stresses and to selectivelysegregate the circulating particles for Withdrawal of the desired fines.

References Cited in the tile of this patent UNITED STATES PATENTS1,305,413 Schutz June 3, 1919 1,570,037 Blum Jan. 19, 1926 1,760,245Lykken Mar. 27, 1926 (Gther references on following page) OTHERREFERENCES Lykken June 2, 1931 Lykken Dec. .5, 1928 Dauber Feb. 7, 1933Sturtevant Jan. 6, 1942 Schaich Jan. 13, 1942 Frisch June 9, 1942 LykkenDec. 8, 1942 10 Wall Ian. 23, 1945 Sheldon May 15, 1951 Lykken Apr. 10,1956 Lyk-ken July 17, 1956 FOREIGN PATENTS France Dec. 16, 1910 "GermanyNov. 11, 1936 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent N09 2 953 5307 September 20 1960 Henry Ga Lykken et a1.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 3 line 58 for "swimmer" read skimmer -g column 4L line 11 for"an" read any Signed and sealed this 11th day of April 1961.,

(SEAL) Attest: ERNEST W SWIDER ARTHUR W. CROCKER Attesting OflicerActing C i sioner of Paten

